2D Floating Box Motion Under The Coupling Effect Of Waves And Tank Sloshing

Recently, clean energy has become a globe issue, and the demand for offshore oil and natural gas is getting popular. The motion response of a LNG or FPSO ship carrying liquid cargo in waves is affected by the external waves and the internal sloshing together. That is, ship motion excites sloshing, while sloshing affects the ship motion in return. This is a complex problem of outer waves, ship hull and inner sloshing coupling, which is important in the design of appropriate tank with capability to withstand sloshing loads and keep good seakeeping of ship. Therefore, this coupling problem has been cared about by ocean engineers.Both experimental investigation and numerical simulation have been carried out by this paper. Single degree of freedom (SDOF) experiments on a2D rectangular hull section containing two identical tanks with different filling conditions have been carried out in a wave flume excited by regular waves. A time-domain numerical model is also established, which consists of two parts. The linear ship motion is simulated using the impulse-response-function (IRF) method, while the nonlinear sloshing flow is solved by a meshless method, the smoothed-partiele-hydrodynamics (SPH) method.First of all, A good agreement between the experimental and the numerical results has been achieved, which shows that the numerical model established by this paper is efficiently in predicting this coupling effect. Secondly, two or more peaks in the roll curve of response-amplitude-operators (RAOs) versus wave frequency have been shown for filling conditions compared to one peak in empty tank case. The first peak occurs around the eigen period of the system consisting the hull and the water inside, while the second peak frequency is very close to the lowest linear eigen frequency of the inside sloshing. Thirdly, sloshing-induced forces are about90degrees phase out of wave exciting forces when the wave exciting frequency approaches the peak frequency of the RAO curve, while180degrees happens when come close to the natural frequency of inside sloshing. Finally,"——" baffles have been added to the tank, the results show that this kind of baffles can restrain sloshing flow effectively, thus causing a dramatic decrease of roll motion, but has little influence on the sway and heave motion of hull section.